This invention relates generally to a clock movement, and more particularly to a clock movement which can detect when an hour wheel and a minute wheel are in predetermined reference positions and correct the time displayed by hour and minute hands by a time zone time difference or by the error in the time displayed.
Examples of conventional clock movements of the kind to which this invention relates are described in Japanese Patent Publication No. 61-118683 and include those which detect when an hour hand, minute hand and second hand are displaying the time twelve o'clock, detect any difference (error) between the time at which this twelve o'clock time is displayed and the time at which a radio time signal or similar broadcast time signal for that hour is received, and, every twelve hours, correct any error in the time displayed by the clock.
In a first example disclosed in Japanese Patent Publication No. 61-118683, as shown in FIGS. 1-2 thereof, when openings in intermediate wheels and in an hour wheel and a minute wheel become aligned once per revolution of the hour wheel, i.e., once every 12 hours, light from a first light-emitting device mounted on a circuit board passes through the openings and is detected by a first light-receiving device mounted remote form the circuit board. The first light-receiving device then outputs a reference position signal denoting that the hour wheel and the minute wheel are in their reference positions. Similarly, once per revolution of the second hand, i.e., once per minute, when openings in an intermediate wheel and a second wheel become aligned, light from a second light-emitting device mounted on the circuit board passes through the openings and is detected by a second light-receiving device mounted remote from the circuit board, and the second light-receiving device then outputs a reference position signal denoting that the second wheel is in its reference position. When the two reference position signals are being outputted at the same time, it is judged that the time twelve o'clock is being displayed.
In a second example disclosed in Japanese Patent Publication No. 61-118683, as shown in FIG. 5 thereof, in order to enable both the light-emitting devices and the light-receiving devices to be mounted on the circuit board, the first and second light-receiving devices are disposed in the same positions on the circuit board as the first and second light-emitting devices are disposed in the above first example, and a single light-emitting device is also mounted on the circuit board. Two light-conducting bodies are used to guide light from the light-emitting device to the positions where the first and second light-receiving devices are disposed in the above first example.
However, with the first example referred to above, there is the problem that because the two light-receiving devices which face the two light-emitting devices are disposed remote from the circuit board, wires have to be provided to electrically connect both of these light-receiving devices to circuitry on the circuit board. The installation of these wires is an awkward and time-consuming task, whereby the clock movement cannot be easily mass-produced. In addition, misalignment between the light-emitting devices and the light-receiving devices can occur during assembly or during use, which makes it impossible for the reference positions to be precisely detected.
In the case of the second example referred to above, there is the problem that, in order to mount the single light-emitting device and the two light-receiving devices on the same circuit board, two light-conducting bodies have to be installed. The light-conducting bodies have to be disposed in a confined space, whereby the construction of the clock movement is made complicated and the cost of manufacture is increased.